MINIMUM AIR QUALITY STANDARDS

[enzed]

Not sure if I'm posting in the appropriate forum.

Much has been said about removal of water and other substances from compressed air for use in plasma cutting. But I have not seen any recommended minimum air quality standards specifically for this activity. Do any exist which we can use at least as a guide or reference point to ensure air quality is of an appropriately suitable standard? I look forward to any responses and recommendations. Enzed

[jimcolt]

Out of the Hypertherm operators manual: Clean, dry, oil-free per ISO 8573-1 Class 1.2.2

Here is a link to some detailed explanations: http://www.parkerstore.jp/phj/catalog/p ... ndards.pdf

In my experience after 38 years with Hypertherm: Connect to your compressed air system and cut metal. If you live in a high humidity region.....you will see water as you religiously drain your compressor every day (you do that, right?). Water in your tank means that water will condense in your air lines. Small amounts (maybe a teaspoon a day draining from your tank) will be handled adequately by the onboard coalescing filter/auto drain (on a Hypertherm). If more than that.....consider a 20' length of copper pipe after your compressor (as an aftercooler) with a downward slope and a low drop leg...install a coalescing filter and auto drain at that point......then take you plasma air from a high point on the end of the copper line. If you are in a tropical climate and cutting at high duty cycles.....consider a refrigerated dryer with auto drain (very little maintenance) or a dessicant type dryer (there are cheap ones that will need replacement or maintenance). If you look at air systems for auto paint spray applications....they are good for plasma too. Often I see users buying small (probably could hold a 1/4 cup of water) desicant filter......if it is 1/4 cup sized and your compressor produces a cup of water......the water will not disappear...if will get through to the plasma.

Last but not least. Some plasma cutter torch designs will destroy an electrode and nozzle with a couple of cups of water. Newer designs (and I speak for Hypertherm) are designed to handle occasional moist air. I see too many people reading and believing online posts about overfiltering , over treating air for plasma cutters. I work with more people that have issues with inlet air starvation (too much filtration/treatment cause air flow restriction) than I do with users that have real water issues that affect consumable life and cut quality.

Jim Colt Hypertherm

Jim Hypertherm

[enzed]

Thank you very much Jim, your advice is not only extremely useful, but it puts the matter in perspective very nicely, and even more so when the ISO Air Quality Standards document (to which you provide the link) is also studied. This clearly shows where is plasma cutting air positioned along the gradient or range of air quality standards. For the first time, I now know what 'clean' means in the context of air quality for plasma cutting.

I was also heading for over-filtration (and perhaps air starvation as a consequence) but now realize that dealing with moisture in air generally does need not be so complex and expensive. Thanks you again and best wishes, enzed.

[herrmc@gmail.com]

- I would like to respond to this thread:

a.) I would like to address Jim Colt.... I have read your article from all the way back in 2013

http://www.achrnews.com/blogs/16-guest- ... ma-cutting

And watched a couple of videos you participated in:

https://www.youtube.com/watch?v=X4_nFpARRRY

https://www.youtube.com/watch?v=HqwUGUWxQZs

--- I thought that others finding this thread might find this info useful.... Thanks Jim, good info.

--- But I DO believe that our cause (excellence in CNC plasma method) can be advanced somewhat by a little more innovation and at least "understanding" ... but setting of some measurable standards.

b.) I really like the premise of how this thread started.....

-- I did just what Jim said.... connected my plasma.... started cutting.... had problems... corrected.... cut.... problems...corrected... cut (vicious cycle).

-- For moisture in my air stream... it has been a continual learning curve (and expense). In addition to learning the dynamics of Compressor operation, dewpoint, the difference of dewpoint under pressure.... Temperature... filters... dryers... I also have learned that the air quality effects a lot more than consumable life ...

-- I drain my tank.... I know that helps... but it isn't enough.
-- I have about 30 feet of steel (black) pipe... that helps cool the air... with drop legs to remove the water... that helps... but isn't enough.
-- I have a Motorguard filter ... that helps... but not enough.
-- I have a refrigerated dryer installed... and an Air Compressor with an aftercooler ... that helps (a lot)..

--- all of that combined enough "Appear" to be enough... but in our Oklahoma climate... with the wild humidity and temperatrure changes, I am quite certain that the quality of my air is constantly changing ... even though the parameters of my air system remain relatively static.

--- And it is anyones guess..... I "guess" my air is good enough... because I am getting plenty of pierces on my consumables, and cut quality is good... and getting no strange shutdowns (loss of arc)...... but then the day comes when I do have problems.... is it the air? maybe... maybe not???

--- I would like this..... A device that I can put inline that will measure 3 parameters "at or near the input to my plasma" (HyperTherm 105).....

1.) Temperature of the air
2.) Dewpoint (moisture content) of the air.
3.) Pressure (during cut)

--- I would like for this device to have the ability to log these settings... (probably not very important... but I would still like it).

--- I would like to have 3 large red LED displays mounted on the wall behind my plasma table that constantly show the 3 measurements ... where I can glance up and "Know" factually about the quality of my air at any given time.... then I can also experiment and learn what minor changes make a difference..... if I start having a strange issue, I can quickly look and know if the quality of the air supply has deviated from normal.....

--- it would also maybe be nice to have 2 more measurements
4.) Atmospheric Dewpoint (input to my Air Compressor).
5.) Temperature ... in my shop ... (maybe also temp outside)....

to be able to tell a little more specifically what factors change ... then correlate them to the performance of my cutting.

--- Most of the above is more than do-able (actually all of the above is very do-able).... maybe just not economically feasible....

--- Pressure input to the plasma is easy....
--- I have found a few companies that sell the sensors and displays to monitor the Dewpoint and the Temperature as well..... they do cater more to larger industrial Air supplies... and their solutions to not scale so well to our small interest.... (a single device using 7.7 scfm of air maximum)..... but they do have solutions.... I have right now been speaking with Vaisala .... and they have given me information... and pricing .... preliminary is around $1,000 ...... I find that to be a little expensive.... but for me probably is worth it.... but I also believe that it should be able to be done much more economically than that.

--- I really look forward to hearing from others with input on this as well.

[herrmc@gmail.com]

The sensor for measurement of the dewpont (made by Vaisala) ..... is a DMT132... and it retails for $493

---- the LED display device is a "Nokeval 301" ... and it retails for $232

.... and there are a host of other options that all bring a $$ amount with them... mostly minimal adds... but some are in the $1xx range

.... this sensor is designed to work with the air after the refrigerated dryer.... adn it's working range is 14*F ~ 140*F (but is optimal at 26.6*F ~ 68*F)


*** below is cut/paste from the description ***
The Vaisala HUMICAP® Dewpoint
Transmitter DMT132 is an affordable
dew point measurement instrument
designed to verify the functionality of
refrigerant dryers. It is especially well
suited for OEM dryer manufacturers.
Direct Measurement
Cuts Costs
Direct outlet air dew point
measurement provides accurate
information about dryer functionality
and is more reliable than the
traditional method of measuring
refrigerator temperature only.
Knowledge of the real dew point
ensures high quality compressed air
at all times and enables customers to
optimize dryer capacity. This helps
to prevent investment in redundant
dryer capacity and avoid unnecessary
maintenance and costly malfunctions.

****

[herrmc@gmail.com]

http://img.en25.com/Web/Vaisala/%7B6d84 ... LOW-v1.pdf

[herrmc@gmail.com]

http://www.vaisala.com/en/industrialmea ... MT132.aspx


Here is the info on the DMT132 ... and it has a picture and specs

- I am not trying to sell this companies products.... just so far it is what I have found.... I would love to find someone with a more manicured solution.... and even better ... a more affordable solution.

[herrmc@gmail.com]

Oh.... and I would also love to be able to measure the flow rate through the air line as well

[jimcolt]

There are hundreds of thousand of air operated plasma cutters installed worldwide. If you have moisture in the air that is affecting consumable life and cut quality you simply add some simple filtration, coalescing filters and / or refrigerated dryers, dessicant driers similar to those used for paint spraying applications. There really is no need to monitor the humidity level in the compressed air system (what will you do once you have the humidity numbers?) or the flowrate (flowrate with a plasma is determined by the nozzle orifice and cut pressure setting). Filtering, separating moisture from air lines is not a costly or difficult process. Jim Colt Hypertherm

[herrmc@gmail.com]

I get all of what you are saying Jim (and respect your position) ... and it has worked that way for me for about 7 years.... I have already added Refrigerated Dryer, Filters etc..... (and it is working)... but there still are anomalies.

Example.... one day I might be cutting a lot and get 500 ~ 600 pierces on my nozzle........ then the next week.... I might be doing the exact same job.... with all the same parameters and get 200 pierces ... and maybe get a little difference in edge quality. It isn't the end of the world... those variable results all still work... but here in Oklahoma (unlike some parts of the country).... we have wild fluctuations in our temperature... and atmospheric humidity has a very wide range..... (even time of day changes them a lot).

-- so what would I do with those humidity numbers ? .... I would try to make note of them on the days when performance was "off the chart good"... and compare them when days were ... less than stellar... and it would allow me to make predictable changes to my air system rather than just guess and change up filtering.

-- Am I willing to invest a fortune in this? (no)..... but if I could get something going at or near say $500 .... I would do it in a heartbeat.... Larger plants are doing this with their air supply ... and finding it to pay off... I just don't know if it can be done economically for a small scale like my shop.... but I think that there is some possibility.

-- One of the thoughts I had about the flow rate..... (I get that it isn't a hugely valuable number).... but I find myself wondering if monitoring that value could give me a little bit of a "health" rating of the nozzle.... example... as the orifice starts to wear (get larger).... I should see a corresponding change in the flow rate .... also if I am getting some sort of restriction ... that should be noticable on the flow rate as well.

-- I am not implying that this is a necessity ...... but for me I think it would interesting... and helpful to turn it more into a science than a voo-doo art. I have already found that I can purchase the components to do this for less than (near) $1,000 ..... for me I am on the fence at this number..... but if I could find something just a little cheaper

[herrmc@gmail.com]

- Also ..... some of what I have been reading ... is that the Refrigerated Dryers by specification are wanting air that is already cooled down somewhat..... that an "Aftercooler" is recommended before the refrigerated dryer...... I am told that most refrigerated dryers to perform to their specifications need air input in the 120* F range... and that most compressors output air at around 150* range (my numbers could be off... didn't go back and re-read... just pulled that from memory).

- In talking with my Air vendor ..... he had said that we can just oversize the Refrigerated dryer to compensate for not having a high quality "AfterCooler" ..... I have a 28CFM Air Dryer (Polar Air - (by Eaton)) ..... It has worked well for me for about 5 years..... but is it still working as good as it used to? How would I know.... if I had a reading of the output dewpoint.... I would have a very good daily indication to the health and effectiveness of how my dryer was working... and my coalescing filter...... I did have one case where the fan on my dryer failed to start..... and it made a difference on the dryer... (and we did not notice this for a while).... the reading would have immediately let us know of a problem with it.

- Also - I find a very big diversity in Air Dryers available.... for example... the Polar Air (Eaton) that I have is relatively in expensive.... (middle of the road)... and I have noticed much less expensive units (different brands)... and I have also noticed more expensive brands.... (I am considering purchasing an FS-Curtis RNP-25 to replace my aging Polar Air dryer..... Those monitoring numbers would allow me to validate and compare if the dryer was as effective as the Mfr suggests (by their ratings and specs).....

[herrmc@gmail.com]

- So this will definitely be a learning experience for me..... still reading, and still learning. Not sure if anyone will have input other than Mr Jim Colt.... and I might have scared him off by now with all my rambling.

- So I have read the ISO 8573-1 standard..... and so when I interpret the air standard requirement from my HyperTherm Manual
-- Page 1-7 .... ISO 8573-1 Classs 1.2.2

> Particulate size must meet the most stringent standard (1)
> Water: Pressure Dewpoint must meet the second most stringent standard (2)
> Oil : class 2

--- so for me right now, I am mainly interested in Water ...... and according to my manual I need -40* Celcius Dewpoint @ 1 Bar (14.5 psi)
> I used "http://www.howelllabs.com/resources/dew ... alculator/" .... and it says that at 80 psi ... the dewpoint requirement would be -25.2* C ... or -13.4* F

---- According to my research ... and Air Dryer can only reach dewpoint levels of around 35* F .......

---- I know that obviously it works with the air from my dryer .... (what the actual Pressure Dewpoint is I have no idea)..... but I think it is safe to say it is not anywhere near -13.4* F

--- I was very interested when I seen that ISO 8573-3:1999 would specify the test method for the measurement of humidity ... and I was eager to read that one..... but my search online shows that I must purchase that one.... and I think it was $134 ??

[jimcolt]

Changes in air humidity are only one cause of overnight changes in cut quality. More often I find inaccuracies in height control as the primary reason for edge angularity, edge roughness and premature consumable failure. As consumables wear, particularly the electrode.....the arc voltage increases when cutting at a fixed height and speed. Better height controls use ohmic surface sensing at the beginning of each cut determine the exact surface location, then do voltage sampling as soon as the x or y axis achieve close to the programmed cut speed. This calibrates the arc voltage / height relationship and maintains correct physical height and cut edge quality. Ohmic sensing also improves pierce height accuracy (dramatically longer nozzle life). Voltage sampling height control (as compared to using a preset voltage number) also will compensate for changes in compressed air humidity (when the humidity of compressed air changes....the resistance of the plasma arc changes, creating a different physical cut height at a given voltage).

Bottom line......most cut quality issues (on Hypertherm air plasma systems) that I find that the user blames on air quality....are related to height control consistency. Air quality can affect height control.....however better height control designs compensate even for poor air quality.

I have been using air plasma system in my home shop for 18 years. No filtration, no dryer, nothing other than the onboard coalescing trap. I routinely get 2500 to 3000 starts on a single nozzle and electrode with consistent cut quality to the end. Proper height control is the reason for my success, and I'll back that with my 39 years of troubleshooting experience working for Hypertherm. My shop iis in New Hampshire with temps ranging from -35 degrees to 100 degrees, and extreme summer humidity levels (June, July, August).

I recommend treating air only when you can physically see humidity spraying from your torch or from an air hose......if using a Hypertherm air plasma. The suppliers of air drying, filtering, moisture traps, etc. would like us all to think otherwise! Jim Colt Hypertherm